Recovery of cyanide



Sept. 21 1926.

LE ROY W. HEFFNER ET AL RECOVERY OF CYANIDE Filed March 5, 1926 l forthe manufacture of concentrated am-- monia or ammonium sulfate, theliquor oi.-l

Patented Sept. 21, 1926.

UNITED STATES PATENT OFFICE.I

LE ROY WILBR HEEENER, or EAST NoRRIsToWN TOWNSHIP, MONTGOMERY COUNTY,AND WILLIAM TIDDY, or 4 JEEEERSONVILLE, PENNSYLVANIA, AssIGNoRs ToRAINEY-woon PRocEss cORroRATIoN, OE NEW YORK, N.,Y., A CORPORATION orDELAWARE.

RECOVERY F CYANIDE.

Application led March 3, 1926. Serial No. 91,889.

This invention relates to improvements in the -recovery of cyanide. fromammoniacal gas liquor.

. In the distillation of ammoniacal liquor ten contains considerableamountsA of cyanide. The present inventiouirelates to an improvedprocess of recovering this cyanide. A

According to the present invention the ammoniacal vapors from the'ammonia sti'll are subjected to a scrubbing treatment, e. g. With acaustic soda solution With the result that the ammonium cyanide or thecyanide compounds are absorbed as sodium cyanide.

The cyanide so absorbed is i. e., treated With ferrous and ferrie ironsalts in a slightly acid solution with resulting formationandprecipitation of Prussian blue, which is obtained as the product ofthe processk and which contains the cyanides in a commercially valuableform. i

In its broader aspects the invention includes the recovery of cyanidefrom the distillation Oi' ammonia carried out to roduce ammonium@sulfate. For examp e, the amount of ammoniacal liquor to be distilled islimited and When the ammonia is recov,`

ered as ammonium vsulfate by the indirect 'processthe ammoniacal vaporsfrom the ammonia still can advantageously be subjected to treatment Withcaustic soda to absorb the cyanide as sodium cyanide, leaving theammonia in a purified condition to pass along to the saturator. Thiswill result in/the production of ammonium sulfate free irombluecoloration. e

l A. particularly advantageous embodiment -of the invention is one inwhich therecovery of the cyanide is combined with the separation orrecovery of phenolic compounds from the ammoniacal gas liquor. `In ourprior Patents Nos. 1,566,795 and 1,566,796;

granted December 22,1925, we have described the process of separatingandv re-o covering phenolic compounds from ammoniacal gas liquors in'which the distillation of liquor is carried out with the. maintenance ofa suliicently high'temperature at the top offthe ammonia still i. e.,around 98 degrees C. or higher to insure driving off of phenolic -alongfor further treatment.

compounds as ammonium phenolate in the ammoniacal gases.

The improved'proces's of the present inventlon can advantageously becombined with and carried out as the process of the said prior patent,the process being in this said patent. K

`When the distillation is carried out to separate and vrecover phenolsin accordance withl the process of our prior patents the same causticsoda absorbent used for absorbing phenol can be used for absorbing thecyanide and the -ammonia passing along to the saturator or to otherplace of absorption or use may be freed both from phenolic com- 'respectan improvement upon'the process of The ammoniacal gases escaping Jfromlthe top'of the ammonia still, either Without or 'Withypreliminarycooling by dephlegmationl are then passedv to the caustic soda absorber.Where reiiuxing is used between the still and absorber( the temperatureshould not be reduced below about 98 degrees C. so as to avoidcondensation of ammonium phenolate. Where, for example, the temperatureat the outlet ofthe vapors from the stillisaround 104 degrees C., thetemperature of the vapors can be reduced e. g. to around 98-99 degreesC. before the vapors pass along to the phenol and cyanide absorber. Theva-V pors that enter the absorber give up their cyanide and/phenol tothe caustic soda :forming sodium henolates and sodium cyanide. Thepurified) ammoniacal gases then' pass The caustic soda absorbent cansuicientlv be maintained at a high,temperature so that further ab-4soption of Water va or does notv take place an so vthat the sai. causticsoda solution 4resul-ting solution will contain both sodium phenolateand sodium cyanide. The use of this absorbing solution can becarried outinvarious kinds of absorbers including absorbers operating under thecountercurrcnt scrubbing principle. .The solutions will progressivelyincreasein phenolic and "cyanide content until they become practicallysaturated and of little 'alue for further absorbent. lVhen absorptionhas taken place to the desired extent a ferrous salt, e. g. ferroussulfate, is added and then the solution is aciditied sutliciently toseparate the phenols which would separate tor the most part as aseparate layer and can be drawn off as one ot the products of theprocess. The

remaining slightly acid solution is then treated With ferrie iron saltsto produce Prussian blue. y

After the solution has been acidiied and the phenolic oils separated andremoved, the mixture of aciditied solutions and iron cyanogen may betransferred to .fi/precipitat- 'ing tank and agitated and heatedWithlive steam to a temperature ot about 8O degrees C. and the ferriesalt added to torm-l Prussianblue. After the precipitationihastakenplace the mixture may be filtered through a lter press to Lcollectthe Prussian blue 'as one oit the products of Athe process. i

Cyanides cantbe profitably recovered in this Way from liquor when thecyanide' -content of the liquor is suliicient, provided sui'licient gasliquor is treated and the cyanides can be recovered in the 'form of Prussian blue as a valuable product of the process. l

The invention will be further described in connection with theaccompanyingdra-W- ing showing in a conventional andA diagraun maticmanner and in the nature ofalow sheet 0r tloW diagram an arrangeirientofv apparatus adapted 'for carrying out the neuv process. It -Willbeunderstood that the iuv-ent'ion. is illustrated by th's'further specicdescription, but is not limited thereto. y In the` accompanying' drawingan nur monia still is shown conventionally made up of a ree'ammoniastill, klime leg and fixed ammoniaestill with a preheater for preheatingthe liquor for the still so that itslnay.: enter the still' at'\ atemperature ;around 98 4degrees C.or higher. From the andcan then be runtop of the free ammonia still the ammo niacal gases containingphenolic.compound-s and cyanide pass to th'e absorber indicated on thedrawing as a caustic Washer'. This may be of suitable. lconstructionsuch 'as a counter-current absorber with the gases lowing upwardly andthe caustic soda so- I lution flowing doivnwardly o r the gases maybubble up through 4the body of the caustic soda solution. The causticsoda in the tank oi' e. g., 1000 gallons capacity isA shownconventionally for supplying j the caustic soda. solutionV tothe'ca'ustio Washer. rIhe phenolic compounds are decomposed withformation of sodium vphenolate and the ammonium cyanide and other.cyanide are absorbed as sodium cyanide. The ammoniacal gases pass fromthe absorber to a sat-urator or place of other treatment or use. 4 Fromthe caustic washer the solution containing the cy-anide and phenolatepasses to a receiving tank of e. g., 3000 gallons capacity and is thendrawn oill as absorbent into `the aciditying tank of e.- g., 2000kgallons capacity and which is provided With a suitable agitator.

Ferrous sulfate' is supplied in suitable 'amount 'from the solution tankof e. g., 400

gallons capacity. Suliuric acid e. g., concentrated acid of 66 degreesyBaume may be supplied from the acid storage tank e. g., ot' about 88gallons capacity in amount required to slightly acidity the solution inthe acidifying tank. The acid solution is permitted to rest to permitseparation ot phenolic compounds, as a separate layer ol. phenolicoil.The solution is then drawn otlin'to' the precipitating tank of e. 3000gallons capacity while'the `separated oils are drawno into a suitableoil storage tank'of e. g., 500() gallons capacity.

` The precipitating tank is provided with an agitator and' with heatingmeans (not shown) vfor heating e'. g., with live steam to a temperatureot about. degrees-C. when iron chloride solution is added from asuitable mixing tank e. 2,1250 gallons capacity, the amount ot ironchloride added 'being suiicient to react with the ironcya'nogen to formPrussian blue. After the". reactiontakes place the 'solutioncontainingthe'precipitat'edyPrussian blue passesito a suitable" filterin which the lPrussian blue is separated and in .w i'chit is Washed. Itcan then be;

driedv and used as a commercial 'produca'y The so'lutionfrom the filterpasses to a vacuum receiver e. g., ot 250() gallons capacity.`

other purpose. K

still are scrubbed with a suitablevalisorbntsolution to Waste or 'usedfor teilig-ailier injuduch Yco Lacasse such as a caustic soda solutionto combine With thel cyanide as sodium cyanide thus purifying theammoniacal gasses or cyanide. The cyanide thus recovered is then treatedby acidifying and by adding iron salts to form Pressian blue so that thecyanide content is recovered in the form of Prussian blue.

It will further be seen that the invention provides an improved processof separating or recovering phenolic compounds from a1nmoniacal gasliquor in which such separation or recovery is combined with recovery otcyanide; and that both the phenolic cornpounds and cyanide can be'simultaneously absorbed from the ammoniacal vapors, and

-the vapors purified therefrom, giving a resulting solution which isthen subsequently treated to recover therefrom the phenolic compounds inthe form of a phenolic oil andthe c anide'compounds in the form ofPrussian lue.

, Vhile we have described the use of a caustic soda solution forabsorbing thc/cyanide or cyanide rphenolic compounds, yet other suitableabsorbent solution can be used in a similai- Way.

We claim:

1 'Tl1e method of recovering cyan-ides which comprises. treating gasescontaining ammonia and cyanides with an absorbing mediumto absorb thecyanides prefercntially from the gas and converting' the absorbedcyanides into Prussian blue.

2. The method of recovering cyanides from ammoniacal gas liquor whichcomprises subjecting such liquor to distillation for the driving oil" ofammoniac-al vapors containing cyanidcs therefrom, treating suchammoniacal vapors' with an alkali solution to con'ibine withthe cyauidesas alkalicyanides, acidi'l'yinfs)r the resulting solution ot cyanide inthe presence ol' a ferrous salt and precipitating' the cyanide asPrussian blue.

3. The method oi' treating'ammoniacal gas liquor which comprisessubjecting the liquor to distillation with i'naintenance of theteniperaturc oli the escapingr vapors in the still of about 98 C. orhigher to drive oil' phe nolic con'ipounds Aand cyanide: compounds withthe an'unouia, treating the ammoniacal vapors with an absorbent iliorthe phenols and cyanide con'lprmnds and thereby separating suchcompounds from the ammoniacal vapors` treatin?,Cr the absorbed compoundsto separate phenolic oils and converting the cyanidcs into Prussianblue.

4. The method of treating ammoniacal gas liquor which comprisessubjecting the liquor to distillation with nmintenance of theteinperature ol' the escaping vapors in' the still at about 98" C. orhigher to drive oil1 phenolic compounds andi cyanide compounds with theammonia, treating the ammouiacal vapors with a caustic soda solution toforni v phenolate and cyanide, acidifying the resultliu;- solution inthe presence oi' a ferrous salt to sepa ate phenolic compounds and oils,adding a ferrie salt to the remaining-solution and heating and agitatingthe same to precipitate Prussian blue.

G. The method of treating gas liquor which comprises subjectingthe sameto distillation in an ammonia still with maintenance of the temperatureof the vapors at the outlet .troni the still at about D80 C. or higherand with sui'l'icient ammonia present in or added to the still to insuresubstantially complete removal of phenolic compounds with the ammonia,treating the resulting" an'nnoniacal vapors with causticalliali'solution to separate phenolic and cyanide compounds l'rom theammonia vapors, acidity ing the resulting solution to set free phenoliccompounds and precipitating" the ':yanides from the acidilied solutionas .Prussian blue.

i. lhe method oi' treating' gas liquor whichcomprises subjecting thesame to llistillatiou in an ammonia still with maintenance ci' thetempcrflture ol' the vapors at the'outlet from the still at about 98o C.or higher and with suihcient anunonia present in or added to the stillto insure sub stantiall y complete ren'ioval of phenolic compounds withthe'ammonia, treating the rcsulting ammoniacal vapors with caustic alhah i solution 'to separate phenolic and cyanide compounds from theammonia vapors, adding,` a ferrous salt. acidiicving,y the resultingsolution to set free phenolic Vcompounds. prec'pitalin;l 'the c vanides`ifrom the acidiied solution as .lflrussian blue, and returning part olfthe purilicd ammonia 'ons from which phenolic anilv cyanide impurticshave been removed to the still to increase the ammonia content. thereof.

8. The method ot' treating aimnouiacal liquors and 'recovering cyanidestherefrom which compr es distillingammonia from such. liquors, treating`the ammoniacal vapors with an alkaline solution, adding a ferrous salt,acidilyiug the solution, adding a, terric salt and precipitating 'thecyanides with heat and agitation in the' form lof Prussian blue.. z

9. rl`hc method ol" treatingY an'iniouiacal liquorsv and recovering'cyanides therefrom which comprises distilling ammonia from, such liquorswhile maintaining the tcnu'lcra lill us l

whereby to set fvee phenolic oils, separab* ing such oils, and treatingthe solution of eyamdeg Wih ferrous and ferrie salts and me of thevapors escaping from the stillyprecipitating the cyanides as Prussianbue with heat and agitation While lilaintaning i temperature of about 80C.

' 10 Iiitest-imony whereofwe affix our Signa- LL ROY WILBUR HEFFNER.WILLI-AM TEDDY.

tures.

